I prefer L2 for jump, X for melee and L3 for booping.
Use speedboost as often as possible (especially with ults)
Try to keep moving, jumping and wallriding to make the enemy frustrated while targetting you.
In the case of being a solo healer (common in lower ranks) use your amp it up for heals only.
As for wallriding, go into practice range and try to hit the bots while wallriding. It has to be a second nature to truly profit from Lucio. Try to switch between heals and speed to get a better feeling of the wallridespeed!
And also, don’t let anything get between you and booping enemies off the map^^
Edit: if there’s a second healer and some teammates are just spawning back in, be their taxi (going back to spawn and speedboost them back to the point)
Just note that your team must be safe at that moment!
I also taxi Mercy quite often since her GA lets her get back fairly quickly.